Torque wrenches are used to ensure that the correct force is used in fastening nuts, blots and other threaded, screw type fasteners that are secured by tightening. Under tightened (i.e., under torqued) treaded fasteners can result in assembled parts becoming loose or coming apart causing damage to parts, premature product failure and creating hazardous or deadly situations for users of the product. Over tightened fasteners are difficult to remove, can cause stripped threads that can be expensive to replace or repair and may not allow adequate space for assembled parts during expansion and contraction due to heat and friction. Over tightened fasteners can also cause torn or broken bolts leading to premature product failure and creating hazardous or deadly situations for users of the product. Specifications for assembly of products often require that screw type fasteners be secured at specific ranges of torque. Those specifications are usually given in foot pounds or the metric equivalent. People use torque wrenches to ensure that screw type fasteners are tightened to product specification.
Tests conducted by Applicant show that between ⅓ and ½ of all new and remanufactured torque wrenches are off calibration by 10-25% from the displayed reading on the device. Furthermore, the discrepancies between the displayed value and the real value may increase over time with continued usage of the torque wrench. The only way to be sure that a torque wrench is calibrated properly is to test it regularly.
Prior art devices for testing torque wrenches are limited. The most common type of device is called a stress tester. These devices are expensive and, often times, fragile since the devices contain a large amount of sensitive electronics and one or more LCD or LED displays. One example of a stress tester is made by Sturtevant Richmont (Franklin Park, Ill.) under the brand name of Veritorq. Another available tester is the Imada digital torque wrench tester made by Imada Corp. (Northbrook, Ill.). Both of these devices retail for well over $1000 dollars.
Therefore, what is need is an inexpensive and reliable device and method for testing the calibration of torque wrenches.